Manufacturing parts from sheet metal normally requires trimming and welding sheet metal panels. In conventional manufacturing processes, mild steel is used because of its ductility and because it is easy to trim and weld. Many new materials have been proposed for manufacturing sheet metal parts, such as deep drawing quality steels, drawing quality steels, bake hardenable steels, dual phase steels, boron sheets, and aluminum alloys. Lightweight material and high strength materials are now being proposed instead of mild steel in the manufacture of vehicles to increase fuel economy. Working with these types of lightweight materials using conventional sheet metal forming tools and welding processes causes substantial problems in manufacturing processes.
In trimming operations, harder materials require more force to trim scrap from the metal panels. In addition, greater clearance may result when trimming higher strength metal panels because of greater forces being applied to the tool. With conventional mild steel, clearance of less than 10% of the material thickness is generally recommended. Additional clearance may result in the formation of burrs, splits and slivers along the trimmed edge of the metal panel. In addition, increased clearance also may result in increased wear of the tool steel edges. Wear of the tool steel edges can be addressed by resharpening the trimmed steel edges or by shimming the trimmed steel insert that increases manufacturing costs.
Another solution proposed is to include elastic scrap support adjacent to trimmed steels to reduce bending and formation of burrs as proposed by Applicant in U.S. Pat. No. 7,197,970. The use of the elastic scrap supports according to Applicant's prior patent is well suited to perpendicular trimming operations. However, if large angle cuts are required to be made by cam operated trim steel tools that may require cutting angles of up to 60°, the effectiveness of the elastic scrap supports is reduced.
In Applicant's prior U.S. Pat. No. 7,810,366, electro-hydraulic trimming, flanging and hemming a blank is proposed, but large volumes of liquid must be provided to the electro-hydraulic tool. The use of large volumes of liquid reduces machine cycle time because of the need to drain and fill the electro-hydraulic chamber. In addition, increased voltage is required to provide sufficient force for trimming, flanging and hemming panels with greater liquid volumes in larger electro-hydraulic chambers. Also, increasing the spacing between the multiple electrodes that are discharged and the location of the area of the panel that is acted upon reduces the pressure available from the electro-hydraulic pulse.
In welding operations, welding aluminum or mixed metals may require applying an adhesive in the joined area to obtain the required bond strength. The addition of an adhesive adds weight and cost to the finished panel and also complicates the manufacturing process. Spot welding operations and other thermal welding techniques rely upon localized melting of the material of the sheet metal panels. Localized melting reduces the strength and may lower the performance of the finished parts. Electromagnetic welding has been proposed to bond aluminum and other mixed metal assemblies. However, electromagnetic welding relies upon coils that have a short life and are costly to replace. In addition, electromagnetic welding is not particularly effective when applied to materials having poor electrical conductivity.
The above manufacturing challenges and problems relating to trimming and joining lightweight sheet metal panels are addressed by Applicant as summarized below.